Brain muscarinic cholinergic receptors are involved in behavioral and cognitive processes. They exist as M1 and M2 subtypes but little is known of their ontogeny and of the development of the second messenger systems associated with them. The overall objective of the proposed research is to determine the identity and behavior of the muscarinic subtypes during neuritogenesis in the model neuroblastoma B35 and B50 cell lines and during the perinatal period in developing guinea pigs. More specifically, we will determine the proportion of M1/M2 muscarinic receptors in B35 and B50 using the selective antagonist pirenzepine and the general antagonist N-methyl- scopolamine. We intend to study the distribution of these receptor types by autoradiography at various stages of the process of neurite extension. Simultaneously, we will determine by autoradiography the presence of these receptor types using the same antagonists in guinea pig brain slices taken from various areas of the brain during perinatal development. Subsequently, we will determine the coupling of the various types of identified receptors with their respective second messenger systems during neuritogenesis in neuroblastoma B35 and B50. A similar study will be carried out at various stages of development on primary cultures of guinea pig brain cells from areas shown to possess M1, M2 or both receptor types by autoradiography.